Short Span Steel Bridges Coatings & Durability
Advanced Steel Grades and Coating Options Can Extend the Life of a Bridge to 100+ Years
The bridge is an innovative multicell A709-50CR bridge girder design installed in Colusa County, CA. Photo credit ArcelorMittal.
While there are several proven strategies for corrosion protection of steel bridges, there is no universal solution. A proper protection system must be chosen to accommodate cost, fabrication and productivity, long-term performance and maintenance.
Additionally, each corrosion protection system must be selected based on the anticipated exposure of the structure to corrosive elements over its lifetime. Options may include:
- Weathering Steel is available in Grade 50, HPS Grade 50, HPS Grade 70, and HPS Grade 100. Weathering steel is a low cost option for corrosion protection. With costs of about $0.04 more per pound than bare steel, the system is very affordable compared to other protection systems. (resource: FHWA Technical Advisory, Uncoated Weathering Steel in Structures)
- A709-50CR (stainless) is a utility-grade stainless steel which performs well in corrosive environments. It should be considered for bridge applications where severe chloride corrosive environments or excessive time of wetness exist. This includes exposure to excessive road salts or marine environments where maintenance is difficult, expensive or injurious to the environment. (resource: ArcelorMittal, A709-50CR Bridge Applications and Fabrication Guidelines)
- Duplex Stainless Steels are premium stainless steels that combine excellent resistance to various types of corrosion (chloride stress corrosion, crevice corrosion, pitting corrosion) with high strength and excellent low temperature impact properties down to -40F. Duplex grades such as 2205 may be used for bridge applications where accelerated corrosion occurs (road salts, saltwater/brackish water) and/or maintenance is costly, unsafe, or inconvenient for drivers. Duplex stainless steels have good formability and weldability characteristics and increase sustainability of bridge design by reducing carbon footprint through reduced lifetime maintenance, increased recycled content, and elimination of painting and coating requirements. (resource: Sustainable Duplex Stainless Steel Bridges)
- Paint (with a zinc-rich primer based coating system) is used by the majority of state highway departments to coat vehicular bridges. Appropriately selected and applied layers or coats of paint over the hot dip galvanize or thermal spray applied zinc or zinc-rich paint is also an option that will extend the service life of the corrosion protection (referred to as a duplex system). (resource: Sherwin Williams, Bridge & Highway Selection Guide)
- Metalizing effectively increases the life of bridges through a process using an electric arc spray gun to apply a thermal spray of molten zinc or zinc/aluminum alloy to steel superstructure members, providing a protective coating. Metalizing is a rugged coating, so damage due to handling is minimized. (resource: American Galvanizers Association, Metalizing)
- Hot-Dip Galvanizing has been successfully used to combat corrosion in bridges since the 1800s. Whether the superstructure of a traffic bridge, the backbone of a pedestrian crossing, or a beautiful truss igniting the landscape; hot-dip galvanized steel provides long-lasting maintenance-free protection for decades. (resource, American Galvanizers Association, Hot-Dip Galvanizing)
Another resource that provides an excellent overview of all corrosion protection systems is Volume 19 of The FHWA Steel Bridge Design Handbook.
For a list of coating and steel durability suppliers, please see Find-A-Supplier on the SSSBA website.
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